HEPATOCYTES FROM METALLOTHIONEIN-I AND METALLOTHIONEIN-II KNOCK-OUT MICE ARE SENSITIVE TO CADMIUM-INDUCED AND TERT-BUTYLHYDROPEROXIDE-INDUCED CYTOTOXICITY

Metallothionein (MT) has been proposed to play an important role in he avy metal detoxication and in the scavenging of free radicals. Effects of MT on the cytotoxicity of cadmium (Cd), tert-butylhydroperoxide (t -BHP) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined us ing primary hepatocyte cultures from control (C57BL/6J) and MT-I and I I knock-out (MT-null) mice. Compared to control-hepatocytes, MT-null h epatocytes had minimal Cd-binding proteins (MT equivalents), but cellu lar glutathione concentration was similar to the control hepatocytes. MT-null hepatocytes were more sensitive than controls to the cytotoxic effects of Cd (50-300 mu M) and t-BHP (125-500 mu M), as indicated by the levels of lactate dehydrogenase released into the medium. Cd and t-BHP also produced more lipid peroxidation in MT-null hepatocytes tha n in control cells, as demonstrated by the abundance of thiobarbituric acid-reactive substances. However, MT-null hepatocytes were equally s ensitive as controls to the cytotoxicity of MNNG (0.5-2.0 mM), suggest ing that MT does not protect against MNNG-induced cytotoxicity. These results support the hypothesis that constitutive MT levels affect the sensitivity of mammalian cells to Cd and oxidative stress.